Extremely high voltages can develop in the vicinity of integrated circuits due to the build-up of static charges. A high potential may be generated to an input buffer or an output buffer of an integrated circuit. The high potential may be caused by a person touching a package pin that is in electrical contact with the input or the output buffer. When the electrostatic charges are discharged, a high current is produced at the package nodes of the integrated circuit. This phenomenon is referred to as ElectroStatic Discharge (ESD). ESD is a serious problem for semiconductor devices since it can potentially destroy the entire integrated circuit.
The duration of the ESD transient is very short, typically in the order of nanoseconds, and the conventional circuit breakers cannot react quickly enough to provide adequate protection. For this reason, it has become a known practice to incorporate ESD devices in integrated circuits. Conventionally, bi-directional diode strings were coupled between the package pins to protect the respective circuit. Other ESD devices such as transistors were also used. The ESD devices were also widely used between power lines to protect the internal circuits coupled between the power lines and to discharge ESD currents to the ground.
Fin Field-Effect Transistor (FinFET) structures may be used for forming the ESD devices. To make the process for forming ESD devices compatible with the formation of FinFET structures, FinFETs were connected to construct the ESD protection circuits, wherein the channels of the ESD FinFETs were used to conduct ESD currents. This approach, unfortunately, faces design and process issues. To provide the high ESD protection capability, a great number of FinFET devices, sometimes as many as over 10,000 FinFETs, need to be connected in parallel. This means that the breakdown of any one of these FinFETs may cause the entire ESD protection circuit to malfunction. The FinFETs thus need to be turned on uniformly.